Ink jet printer technology continues to improve to provide faster printers which produce higher quality print. In order to achieve these goals, printhead materials, designs and manufacturing procedures continue to change and evolve. In newer printhead designs, the nozzle plates contain smaller, more closely spaced nozzle holes and increased numbers of nozzle holes per nozzle plate. As the size of the nozzle holes decreases and the need for increased production increases, it becomes increasing difficult to provide relatively inexpensive printheads which function to provide quality print over the life of the printhead.
One of the problems which may occur during a printing operation is that ink tends to accumulate on the nozzle plate surface adjacent the nozzle holes. The accumulated ink can, over time, partially block and cause misdirection of ink droplets ejected from the nozzle plate or, in a severe case, totally block ink ejection from the affected nozzle hole. An excess accumulation of ink on the nozzle plate adjacent a nozzle hole during firing of a nozzle is often referred to in the art as "flooding" since the ink may actually accumulate to the point that it covers the nozzle holes. Another accumulation of ink on the nozzle plate is the result of ink pooling. "Pooling" is defined as the accumulation of ink on the nozzle plate when a "tail" of ink forms as the ink droplet is ejected and the ink tail breaks away from the main droplet and deposits back on the nozzle plate. Pooling of ink does not necessarily occur only adjacent the nozzle holes and may occur anywhere on the nozzle plate.
In addition to interfering with ink ejection from a printhead, ink accumulation on a nozzle plate of a multi-color printhead whether from flooding or pooling may result in ink color mixing. As a result of ink color mixing, the ink droplets ejected from affected nozzle holes may not provide the intended color dots thereby reducing print quality. As nozzle holes and their associated ink ejection heaters become smaller and the distance between adjacent nozzle holes is reduced to provide higher quality, faster printing, the effects of ink accumulation or flooding of the nozzle plates becomes a more important factor in the operation of the printer.
Attempts have been made to control nozzle flooding and pooling by applying certain fluorocarbon coatings to the nozzle plates. While such fluorocarbon compounds may possess the desired anti-wetting properties, they generally require the use of an intermediate bridging material capable of bonding the fluorocarbon compound to the nozzle plate material. Use of an intermediate material in addition to the fluorocarbon compound involves additional processing steps which increase the manufacturing cost of the printheads. Furthermore, some of the coating materials presently available often require relatively thick coatings ranging from about 0.3 to about 2 .mu.m. Despite the relatively thick coating, the coatings are not sufficiently durable and may be readily removed or rendered ineffective by techniques used to clean the printheads long before achieving the expected printhead life. Because the coatings are relatively thick, they may also interfere with the nozzle holes causing printhead operational problems.
In addition to the fluorocarbon coatings, other coatings which have been applied to components of the printhead for various purposes have been observed to result in covering the nozzle holes and thereby interfere with the operation of the printhead. Such coatings are typically applied during one or more steps in the manufacturing process and include adhesives, epoxies, silicones, polyurethanes and the like which are applied to protect electrical components of the printhead from corrosion caused by the ink.
It is therefore an object of the invention to provide an improved printhead for an ink jet printer.
Another object of the invention is to provide a nozzle plate having reduced ink flooding and pooling tendencies.
A further object of the invention is to provide a method for making a nozzle plate for an ink jet printer.
Another object of the invention is to provide a coated nozzle plate which avoids disadvantages of conventionally coated nozzle plates.
Still another object of the invention is to provide a nozzle plate having a substantially durable surface-energy modifying coating.
Another object of the invention is to provide a coating technique for applying a surface-energy modifying coating to selected areas of a nozzle plate.
Another object of the invention is to provide a nozzle plate having an ink repellent coating in a pattern which substantially reduces ink flooding, pooling and ink color mixing.